Heavy mineral and zircon age constraints on provenance and correlation of the Sherwood Sandstone Group (Triassic) in the eastern Wessex Basin, UK

Heavy mineral and zircon age data demonstrate that in the Sherwood Sandstone Group of the Marchwood-1 and Southampton-1 boreholes, on the eastern margin of the Wessex Basin, sediment was supplied from both the south (Variscan highlands) and the east (recycled Old Red Sandstone). Interplay of these two sources led to a well-defined heavy mineral stratigraphy in the area. However, the Sherwood Sandstone Group in the Wytch Farm oilfield, towards the centre of the Wessex Basin, contains only sandstones derived from the Variscan highlands to the south and lacks significant amounts of recycled Old Red Sandstone detritus. The equivalent sandstones (Otter Sandstone Formation) on the western margin of the Wessex Basin have a different provenance to both the central and eastern parts of the basin, since they almost entirely lack input from Variscan granitoids. Heavy mineral and zircon provenance data therefore demonstrate sediment input from a number of discrete source areas into the Wessex Basin during the Early and Middle Triassic, and that the ‘Budleighensis River’ system may not have been a single river, at least in the southern Wessex Basin area. It is also evident that provenance-based correlation schemes such as heavy mineral analysis or whole-rock geochemistry should be used with caution over long distances and require careful evaluation of lateral changes in provenance.